A typical swash plate type compressor as disclosed in, for example, U.S. Pat. Nos. 3,801,227 of Nakayama and 3,955,889 of Nakayama et al, has a pair of horizontal axially aligned cylinder blocks which forms a combined block. Inside the combined block are formed axially extending cylinder bores, the cylinder block being closed at both ends by front and rear housings, via valve plates. Centrally passing through the combined block, a drive shaft is rotatably supported by suitable bearing means. To the middle of the drive shaft is fixed a swash plate operatively connected to, via ball bearings and shoes, double acting pistons slidably fitted in the cylinder bores. Thus, the rotating of the swash plate causes reciprocal compressing motion of the pistons within the cylinder bores. The front and rear housings are formed with refrigerant suction chambers and refrigerant discharge chambers, which are interconnected with the cylinder bores and are connectable to an outside air conditioning circuit by means of appropriate refrigerant flow pipelines. The typical swash plate type compressor is provided with means for lubricating the swash plate and movable or slidable parts of the compressor, such as bearing means, ball bearings, shoes and pistons. According to this lubricating means, oil separated from oil suspended refrigerant is distributed toward the above-mentioned movable or slidable parts, without employing an oil pump means. Some typical swash plate type compressors are also provided with means for introducing a part of all of the oil suspended refrigerant into a swash plate chamber in which the swash plate is rotatably accommodated, so that the oil suspended refrigerant per se contributes to lubrication of the swash plate, ball bearings and shoes. The above-mentioned lubricating means employing no oil pump means is very advantageous for reducing the size and weight of the typical swash plate type compressor. On the other hand, the above-mentioned lubricating means is defective in that before the running speed of the typical swash plate type compressor reaches a given high speed range, the amount of the oil suspended refrigerant returned from the air conditioning circuit to the compressor is very small. Therefore, lubricating oil sufficient for appropriately lubricating the swash plate and the diverse movable or slidable parts of the compressor is not acquired. Particularly, achieving continuous appropriate lubrication of the contacting portion of the shoes and the swash plate is very difficult. This is because, during the operation of the compressor, a very large surface pressure reaching 100 through 300 kg/cm.sup.2 acts in said contacting portion, and also, because the shoes perform very complicated motions during the operation of the compressor, whereby the relative position of the shoes with respect to the surface of the swash plate frequently varies. That is, the above-mentioned large surface pressure together with the complicated motion of the swash plate prevent the formation of a film of the lubricating oil in the contact portion of the shoes and the swash plate. As a result, direct contact of each of the shoes and the swash plate without intervention of the film of the lubricating oil occurs generating a high temperature friction heat. Therefore, smooth operation of the compressor is prevented, whereby the compressing efficiency of the compressor is decreased. Further if the generation of the high temperature friction heat continues for a long time, seizure of the shoes is caused, whereby the compressor will finally be broken.
Additionally, when the typical swash plate type compressor is applied to the air conditioning of a vehicle, the compressor is usually placed in the engine compartment of the vehicle. Therefore, the compressor is subjected to high temperature. As a result, the compressor is heated up. Therefore, the viscosity of the oil suspended in the refrigerant is lowered, whereby the lubrication effect of the oil is necessarily degraded. This degradation of the lubricating effect of the oil is also one cause for occurence of the direct contact of the shoes and the swash plate which causes a reduction in compressing efficiency of the compressor or breakage of the compressor
With the above-mentioned typical swash plate type compressor, the shoes are generally made of materials selected from a metal and an alloy. The choice of the materials of the shoes depends on the material of which the swash plate is made. In the case where the swash plate is made of ferrous metal, the shoes are made of ferrous metal coated with a layer of an alloy of copper and lead, having a high resistance to wear and seizure. In the case where the swash plate is made of an aluminum alloy, the shoes are made of one of an aluminum alloy containing 14 through 30 percent silicone and ferrous metals which have a high resistance to wear, and have a high mechanical strength, respectively. However, the shoes made of aluminum alloy containing 14 through 30 percent silicone are defective in that the resistance to a mechanical shock applied to the shoes during the operation of the compressor is low, and resistance to burning is also low as long as the typical swash plate type compressor employs the afore-mentioned lubricating means with no oil pump. On the other hand, the shoes made of a ferrous metal or of a ferrous metal coated with a layer of an alloy of copper and lead is defective in that the weight of the shoes become large, thus increasing the weight of the typical swash plate type compressor. Further, the large weight of the shoes prevents the shoes per se from being smoothly moved during the operation of the compressor.